know the master of the arabian sea 2011

7/28/2019 Know the Master of the Arabian Sea 2011

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Life Cycle

Generally, females grow faster than males. The duration of

life cycle in dwarf form of S. oualaniensisis estimated as 6 months

and middle-sized as well as giant forms as one year. The largestdaily increment in length in the middle-sized form is 1.0 mm, while

in the giant female it is 3.8 mm. The monthly production of 1 year

old giants are 9 times that of middle-sized squids of the same

age.

S. oualaniensislive in the water column undergoing diel vertical

migrations up to 1000 m depths. Larvae are planktonic, juvenilesare often associated with the continental slope. They avoid the

bottom of the sea even in day time. In the continental slope area,

while they descend to the near-bottom layer, they remain 2-3 m

away from the bottom.

The form, and structure of squid mantle, arms, funnel and

fins, their changes during ontogeny characterize these squids as

powerful swimmers for which high horizontal speed is important


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than maneuverability. In general, movements are characterized

by high cruising speed (3-10 km/h; ML 15-35 cm) and high rush

speed/ burst swimming (25-35 km/h). Maximal locomotory activity

is inherent in young animals of ML 3-10 cm. Juvenile Sthenoteuthis

can reach such high speeds that they can leap out of the water

and fly some distance in the air (with tail first). During the flight,

S. oualaniensisextends thin protective membranes on the III arms

and use them as a second fin (functioning as caudal fin).

Locomotory activity decreases strongly in large squids of ML

greater than 45-50 cm.

Vertical distributions change during growth. In the Arabian Sea

giant forms have been observed between 400-1100 m depths in

the daytime which migrate to 50 to 150 m at night time. In contrast,

medium sized females have been observed at 50-200 m in the

day and at depths of 0-100 m in the night. The middle sized form

and young squids occur near the surface. Medium sized

S. oualaniensis(27 cm) often do not form schools.

Vertical distribution of S. oualaniensis; 1 - Isolated individuals2 - High density

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Temperature(C)


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Depths occupied by this species are low in oxygen.

S. oualaniensis has a very high metabolic rate (standard

metabolism of 348 ml O2/kg/h) that exceeds that of many fast

swimming oceanic fishes. Common with other squid species,

energy metabolism is based mostly on protein: however, in S.

oualaniensis, during metabolism a considerable proportion of the

protein is catabolised anaerobically, thus enabling these squid to

inhabit zones of very low oxygen concentration.

Studies suggest that the fishing ground of squid was closely

related to the marine environmental variables such as SST, sea

surface height (SSH), wind, chlorophyll aand zooplankton. The

optimum SST of the fishing ground is 25-28C. Most high-yield

fishing grounds were distributed in the waters near sea surface

height anomalies, SSHA


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Graphicrepresentationofoceanicsquidlifec

ycleshowinginfluen

ceofenvironmental

factors


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Squid Diets - What do they eat?

Fast growth rates and high metabolism indicate the

requirement of high food intake. S. oualaniensis is an active

predator with a wide food spectrum varying geographically as wellas with mantle lengths.

In the stages of paralarvae and early juveniles, the squid mainly

predate on crustaceans. Young feed mainly on amphipods,

euphausiids and fish larvae. On the fishing ground of high daily

catch (over 5 tonnes), zooplankton mainly consists of

Chaetognatha (average biomass of 9.18 mg/m), Copepoda(2.32 mg/m) and Mysidacea (1.38 mg/m). These three species

were also found in the stomachs of squid and could be

considered as indicator species for a squid fishing ground. In

the Arabian Sea, the squid of larger than 20 cm ML fed mainly

on small flying fish. As the size of squid increased, the smaller

squids S. oualaniensisbecame progressively more important

in the diet and by 40 cm ML, squids comprised more than 50%

of the diet (extreme cannibalism).

Oceanic Squid Flying fish


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Early juveniles are active-grazing predators, late juveniles and

middle-sized squids are predator-pursuers, while large-sized adults

are attacking predators. Nevertheless, the giant females of

S. oualaniensisin Arabian Sea consume mainly myctophids, which

are numerous and inactive in the layer 100-200 m, hence they

remain as active-grazed predators instead of large nektonic

predators.


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Predators - Who eats them?

The early juveniles and paralarvae of squids are the prey for a

wide variety of predators including small squids, large chaetognaths,

jellyfishes, carnivorous fishes etc. Squid juveniles from 3-10 cmare prey to large squids, tunas (skipjack tuna, yellowfin tuna, wahoo,

bigeye tuna) dolphin fish, snake mackerel (Gempylus serpens),

lancet fish and small sharks. Main predators of middle-sized squids

are dolphins, swordfish and some active species of sharks. Large-

sized squids are inaccessible for tunas and they have fewer

predators: adult swordfishes, dolphins, toothed whales and large

sharks. A variety of studies indicated the presence of S. oualaniensisin the stomach of various predators.

In Arabian Sea, large oceanic predators rarely occur, therefore

the oceanic squids, owing to its high abundance, large size, short

life span, fast growth and high food ration almost completely

monopolize the trophic niche of the top predators. Hence, they

are called as the Master of the Arabian Sea.Some of the major predators of S. oualaniensis are given on page 15.


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Reproduction & Spawning

In S. oualaniensissexes are separate. Female reproductive

organs consist of ovary, with thin walled as well as glandular

portions; the paired nidamental glands and seminal receptacles.Ripe eggs are pinkish or raspberry coloured. Males have a unilobed

testis and the male genital duct is a white, fluid-filled sac in the

posterior end of the mantle. Sperms are stored in thin tubes

(spermatophores) in an elongated sac behind and along the left

gill.

There is indirect evidence that S. oualaniensis is a multiplespawner where intermittent spawning occurs over an extended

period. Spawning lasts for 1-3 months at a relatively stable level

without a decrease in feeding rate, with significant growth. The

frequency of spawning episodes within this period are unknown.

Accumulation of eggs in the oviducts is a continuous process.

Spawning is not linked to the bottom and occurs in epipelagic

zones. Spermatophores are stored for a long period in seminal

Spawning ground of oceanic squids located in the Arabian Sea


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Map showing juvenile abundance near Lakshadweep Islands

during post-monsoon period

receptacles on the buccal membranes in females consequent to

mating. Potential fecundity depends on the adult female size

varying from 0.3 to 22 million eggs and relative fecundity ranges

from 3,000- 7,000 oocytes per g body weight.

Egg masses of S. oualaniensisconsist of a translucent mucus

in which many pale crimson eggs of 0.72-0.86 mm are dispersed

at a density of about 1-2 eggs/cm3 (maximal volume of 25 l).

In S. oualaniensis, spawning grounds have been located in

the seas around Lakshadweep Islands during post-monsoon. After

the spawning period, juveniles are abundant in the surface watersat densities ranging from 0.5 to 1.8 million numbers/km2 (See map

below).


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Composite abundance map of oceanic squid Sthenoteuthisoualaniensisin the Arabian Sea during 2010-11

Fishery & Stock Abundance

The purple-back flying squids are distributed in open oceans

and are rather scattered; this has impeded their commercial

exploitation. In the North Pacific, historic fishing activity forS. oualaniensisoccurred predominantly off Okinawa, Taiwan,

Vietnam and Hawaii where it is dip-netted or jigged at

the surface during day and night. The species supports

local fisheries from June to November in Okinawa and from

March to November in Taiwan, with peak fishing from May to

August.China has successfully exploited some important oceanic

squids since 1989 from around the world. In 2005, a small-scale

Chinese commercial jigging fishery for S. oualaniensisstarted in

the Arabian Sea, yielding more than 5000 t in production. Fishing


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occurs predominantly by automated jigging using lights to attract

the squid. India is now making attempts to tap this resource and a

composite fishery abundance map is shown on page 18. These

are results of planned jigging surveys carried out during 2010-11.The main period of abundance is for 6 months from October to

March with peak during December - January.

The stock abundance of S. oualaniensishas been worked

out based on scientific surveys in the Arabian Sea during 2010-11

and rendered in GIS format. Many areas between the

Lakshadweep Islands show abundance in excess of 5 tonnes/km2 during the post and pre-monsoon periods.

The total stock of S. oualaniensis in the worlds ocean is

estimated to be between 8-11 million tonnes. Studies indicates

that S. oualaniensis dominates the epipelagial zone of the

Arabian Sea both in number and biomass and that the mean

biomass is estimated as 4.5 t km-2

. The most promising regionfor a large-scale fishery of S. oualaniensis is the Arabian Sea

with the fishable stock estimated as between 1.0 and 1.5 million

tonnes.


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Acknowledgements

We are grateful to the funding support received from National

Agricultural Innovation Project (NAIP) of the Indian Council of

Agricultural Research (ICAR), New Delhi through the ProjectUtilization strategy for Oceanic squids (Cephalopoda) in Arabian

Sea: A Value Chain Approach.

We are also thankful to the Director, CMFRI, Kochi for the

facilities.


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know the master of the arabian sea 2011

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